Piezoelectric Bimorph Elements Research Articles

A precise rotary positioner driven by piezoelectric bimorphs: Design, analysis and experimental evaluation

A precise rotary positioner driven by piezoelectric bimorph elements with simple structure and high resolution was proposed, fabricated and tested in this work. The dimensional design was completed according to the theoretical model, and the simulations were conducted with finite element method. A prototype and an experimental set-up were fabricated to conduct some experiments. The experimental results showed that the positioner had a small mass of 20.5 g, and the output angle fitted a good linear relationship with the exciting voltage. Besides, the repeatability was measured as 0.180″ (0.873 μrad), and the resolution was higher than 0.0252″ (0.122 μrad), which reflected the high precision of the positioner. The dynamic performances were measured and the load characteristic was calibrated as well. Based on good extendibility, more bimorphs could be added to improve the load capability or increase the motion stroke. The proposed positioner had a good prospect in the field of precise rotary positioning.

Modeling a piezoelectric cantilever beam with Simscape

Previous work developed a lumped parameter model in Simscape for the transverse vibration of a thin bar [C. J. Childs and S. C. Thompson, J. Acoust. Soc. Am. 145, 1895 (2019)]. The current presentation expands that to include a layered bar, perhaps of different materials, and includes the electromechanical coupling for the case where the layers may be piezoelectric materials. This allows modeling such devices as the crystal or ceramic microphone that uses a piezoelectric bimorph element, and thin film piezoelectric cantilevers under consideration for vibration energy harvesting applications. While this paper uses Simscape for its examples, modeling these features in Modelica is equally possible.

Ultra-Low Wind Speed Piezoelectric Windmill

We report an ultra-low start-up speed windmill that consists of a 72 mm diameter horizontal axis wind turbine rotor with 12 alternating polarity magnets around its periphery and a 60 mm × 20 mm × 0.7 mm piezoelectric bimorph element having a magnet at its tip. This wind turbine operates at very low Reynolds number of around 2×104, but still it has reasonably high power coefficient of about 11% at the optimal tip speed ratio of 0.7. It was found to produce peak electric power of 450 μW at the rated wind speed of 4.2 mph. An extremely low start-up wind speed of 2.4 mph was achieved by operating the bimorph in actuator mode.

Piezoelectric composite lattices with high sensitivity

Lattice structures are presented with a piezoelectric sensitivity, d, much larger in magnitude than that of material comprising the lattice ribs. Large sensitivity is achieved by using piezoelectric bimorph elements as ribs; these bend in response to electric input, giving rise to a much larger displacement than for axial elements. Complex electrical connectivity is helpful, but not necessary; surface contact can be sufficient. Lattices are amenable to piezoelectric vibration damping. Piezoelectric sensitivity can be arbitrarily large and is unbounded.

ACOUSTIC VIBRATION GENERATING ELEMENT

In an acoustic vibration generating element, a piezoelectric bimorph element or unimorph element is covered with a covering member of a flexible material at least on two surfaces perpendicular to a thickness direction. The covering member may be provided with a plurality of V-shaped grooves so as to improve a generated vibrating force. Alternatively, the covering member may be provided with an air chamber in the vicinity of a surface of one side so as to prevent sound leakage. Further, the covering member and an earhook may be integrally formed by the flexible material so as to achieve a light-weight acoustic vibration generating element suitable for a bone conduction speaker.

High-sensitivity in-plane vector magnetometry using the alternating gradient force method

The alternating gradient force magnetometer is a highly sensitive tool particularly suited for thin films magnetometry. The measurement technique is based upon the alternating force generated on a magnetized sample by a set of field-gradient coils. The so-induced sample oscillation is directly proportional to the sample’s magnetization. High sensitivity measurements are achieved by mounting the sample at the end of a cantilever attached to a piezoelectric bimorph element, and by tuning the excitation frequency close to the mechanical resonance of the sample-cantilever assembly. Here we describe a new design that allows to measure both in-plane components of the magnetization of a thin film sample, for any direction of the external magnetic field within the sample’s plane. By rotating the sample-probe assembly, we find the output signal to be proportional to the projection of the alternating force along the sense axis of the piezoelectric bimorph. Besides, the resonance frequency of the system remains unchanged. Thus, hysteresis loops can be measured accurately for various angles between the applied field and an in-plane anisotropy axis. The signal only vanishes when the alternating force is orthogonal to the bimorph axis. Moreover, we have designed a set of two pairs of gradient coils, whose axis are orthogonal to one another. By varying the excitation current within these two pairs of coils, it is possible to rotate the alternating gradient direction, to detect magnetization components along or perpendicular to the external field.

Wide range temperature compensated cryogenic scanning tunneling microscope

We describe a compact scanning tunneling microscope using piezoelectric bimorph elements to achieve a large scanning area of 20 μm2 at 4.2 K. This instrument provides inherent temperature compensation, compatibility with a high magnetic field environment, and a novel means of rough sample–tip (z) adjustment.

Mechanical stimulation and micromanipulation with piezoelectric bimorph elements

Piezoelectric bimorph elements are versatile and inexpensive electromechanical transducers which may be used to construct fast mechanical stimulators and finely controlled micromanipulators. The mechanical stimulators described provide continuously graded displacements ranging from nanometers to about a millimeter, or forces equivalent to 0–7 g. Appropriately designed units can produced small step displacements complete within 100 μsec. Micromanipulators are described which generate 3-dimensional motion under remote electrical control and which enable positioning within a few tenths of a micrometer. They are sufficiently stable to hold glass microelectrodes for cell penetration or probes for microdissection. The two significant drawbacks of bimorph elements are mechanical resonance and continued movement following displacement, or ‘creep’, but methods have been developed to compensate for these. A number of methods are available to measure motion of bimorphs with spatial resolution of 10 nm and temporal resolution of 2 μsec in favorable situations.